The present invention relates generally to a suspension trailing arm and a method of making a suspension trailing arm. More particularly, the present invention relates to a cast or forged suspension trailing arm, a suspension assembly incorporating a trailing arm and method of securing an axle locating feature of a suspension trailing arm to an axle.
Heavy commercial vehicles typically employ trailing arm suspension systems, particularly in relation to the axles of trailers of articulated vehicles or potentially rear axles of rigid body vehicles.
Heavy commercial vehicles (including trucks, buses and coaches) can be distinguished from light commercial vehicles (such as vans) and light passenger vehicles due to one or more of the following characteristics: 1) a laden weight in excess of approximately 3.5 tonnes and 2) the use of air actuated brakes as opposed to hydraulically actuated brakes (because air actuated brakes are better able to withstand the increased heat generated by the repeated braking of a vehicle having a weight in excess of approximately 3.5 tonnes).
Such vehicles (including trailers) also typically employ a pair of spaced parallel beams that run the length of the vehicle and act as the chassis upon which the vehicle body is mounted.
When used in heavy commercial vehicles, the trailing arms are typically pivotally mounted to chassis beams of the vehicle at the front of the arm. The trailing arm extends rearwardly (i.e., towards the rear of the vehicle) to a mounting position for the axle and then further rearwardly to a mounting surface for an air spring that is itself mounted between the trailing arm and a vehicle chassis. Axles in such vehicles are typically substantially rigid beam-type axles (i.e., axles that extend between the spindles upon which wheels at opposite sides of a vehicle are mounted). In some circumstances, the orientation of the arms may be reversed so as to pivot at the rear of the arm, in which case they are known as “leading arms.” For the purposes of this specification, the term trailing arm should also be understood to encompass leading arms.
Known heavy vehicle trailing arms are typically constructed either from solid spring steel and provided with U-bolts and plates to connect an axle to the arm, fabricated steel plate which is then welded to an axle or axle adapter, or a hybrid of the two aforesaid types. An example of a fabricated trailing arm is disclosed in U.S. Pat. No. 5,639,110 (Pierce et al.). Both prior art types provide a rigid connection between the arm and the axle in order to resist bending, but have a resilient connection between the chassis and axle, either by the flexing of the spring steel trailing arm or by the flexing of a large elastomeric bush (resilient bearing) in the end of a fabricated trailing arm. This enables articulation forces induced during vehicle use to be taken up while maintaining tracking and roll stability. It has typically been considered necessary for fabricated trailing arms for use in heavy commercial vehicle applications to be manufactured having a closed box-section profile to impart sufficient strength to the arm to withstand vertical bending forces, as well forces caused by cornering, vehicle roll and travel over uneven surfaces.
Two prime disadvantages have been identified in known trailing arm designs. First, the known manufacturing techniques often place restrictions on the shape of the trailing arm, which in turn restricts the positioning of additional components that are mounted to the arms, such as brakes, air springs, dampers and pivot bushes. This may lead to the suspension packaging (i.e., its space requirement) being inefficient. Second, known types of trailing arm designs are time consuming and hence expensive to manufacture, either due to the welding or fastening of the various components that constitute the trailing arm together or due to the fastening or welding operations required to secure the trailing arm to an axle.
It is known from U.S. Pat. No. 5,203,585 (Pierce) to make a cast trailing arm type suspension for heavy vehicles. However, a separate subassembly is provided to mount the axle to the arm.
The present invention seeks to overcome, or at least mitigate, the problems of the prior art.